Outdoor positioning systems, such as global positioning system (GPS), have been widely applied in car navigation systems to localize a car or a person outdoors. However, indoor positioning systems still have many problems to be solved. The indoor positioning systems are subjected to that (1) electromagnetic signals are easily sheltered in the indoor environment such that satellite signals cannot be received and (2) the changing indoor environments (such as indoor objects and persons) easily.
The present indoor positioning technology has two types: an external positioning system and an internal positioning system. The external positioning system, for example, estimates the location of an object (for example a robot) in a space based on a relative relationship between an external sensor and a receiver of the robot. In the internal positioning system, for example, a sensor is located in the robot and the information sensed by the sensor is compared with a built-in map to estimate the location of the robot in the space.
The external positioning system has a high positioning speed, but requires an external sensor which is installed beforehand. Once the external sensor is moved or sheltered, the system cannot do positioning any more. When applied in a large area, the external positioning system requires more sensors and thus much more cost.
The internal positioning system has a lower positioning speed but a larger extensibility. Even in the environment that changes easily, as long as there exists at least one environment feature for positioning, the internal positioning system can still do positioning. However, the internal positioning system needs to build a map of the indoor environment before positioning.